1. Field of the Invention
The present invention relates to a switching power supply device having a switching element, a coil or/and a transformer.
2. Description of the Related Art
A heat sink having plural heat radiation fins is provided to a switching power supply device in which circuit parts containing a switching element, a coil or/and a transformer are mounted on a board. Circuit parts having a large amount of heat generation such as the switching element, etc. are fixed to the heat sink. The heat sink radiates heat generated by the circuit parts through the heat radiation fins. In this type of switching power supply device, it is considered that the heat radiation fins are directly exposed to (barely arranged at) the outside of the switching power supply device to radiate the heat to the outside. However, this configuration makes it unavoidable to design a housing (case) in a large size in order to increase a radiation efficiency. Therefore, a technique of making air flow into a case by using an air suction fan or/and an air blow-out fan to cool circuit parts by a forced air-cooling system and blowing out high-temperature air in the case to the outside to radiate heat has been proposed to satisfy an requirement of miniaturization of the switching power supply device (see JP-A-2005-124322).
However, when the circuit parts are cooled by making air flow into the case with the air suction fan or/and the air blow-out fan according to the forced air-cooling system, dust such as minute metal pieces, dirt or the like is sucked from the surrounding into the switching power supply device together with air. Furthermore, the dust sucked into the switching power supply device is liable to be trapped in the switching power supply device. When the dust such as the minute metal pieces, dirt or the like is accumulated in the power supply, the probability of occurrence of a failure caused by external factor increases. Accordingly, there is a problem that the switching power supply device may have a short lifetime.